Accelerating epoxy with heat

[Paul Eastham]

Hey fiberglass experts,
I'm using West System epoxy with the slow hardener for all of the usual non-structural RV things: emp tips, airbox, miscellaneous filler, etc.

I noticed that my work would cure (or nearly so) if I put it out in the sun for an hour, instead of the usual 24+ hours. Taking that a step further, I have used a little bit of heat gun to accelerate small micro buildups and the like, with pleasing results.

I'm curious if there's much downside to doing this. The only thing I could think of is an inhalation hazard from the accelerated outgassing. This is mostly a theoretical question for me, since I don't really care about the structural integrity of my micro fillets

Paul

[frankh]

and stuck some parts in the oven...Much to my Wife's dispair...Hardens in about 3 minutes.... Hey the oven was warm with her pies she was cooking so why waste free energy?

I've seen some guys use microwave ovens too.

Sure hope there is no downside....I've cooked a lot of parts this way.

Frank

[Mike S]

This is hearsay only--------I am not a chemist, but I have been told that part of the strength of epoxy is that it forms "Long chain" molecules while curing----and that accelerating the cure can interfere with this process.

Any body out there with a chemistry backgorund have input??

Mike

[jcoloccia]

There's no real downside as long as you're not going nuts with it. I wouldn't use a heat gun because it's way too easy to overheat the epoxy and cause poor curing (or damage/warp the underlying layups). If you do use a heat gun, use it very carefully.

In general, though, there are different formulations of epoxy that are designed to be cured in an oven. Many of them use a combination of UV/Heat curing and are designed as such (they're stored in a very cold freezer).

Leaving it out in the sun is a FINE idea. A couple of heat lamps is probably a OK too. Unless you really know what you're doing, I'd stay away from the heat gun and ovens. Since none of this is structural, I guess you can tolerate some weakening.

If all you want to do is get the micro to flow a little bit better, a hair dryer works just as well. A trick I use to fill pin holes is to spread raw epoxy over the piece and then hit it with a hair dryer or heat gun (VERY gently) and it magically flows into the holes and fills them.

Bottom line: Except for micro, and filling pin holes, I wouldn't heat it much past 100 or 120F (equivalent of a really hot summer day out here in the Antelope Valley) unless you really know what you're doing.

[mdredmond]

You can call Gougeon Brothers (West) at 866-937-8797 and they'll answer whatever questions you have. They were extremely helpful with lots of (free) technical advice for a major structural repair I made to my boat.

[gpiney]

John is right about the 100-120F range. Make a box out of some Home Depot insulating foam sheets. Put a 60Watt lightbulb in it.
Use a meat thermometer to monitor the temp. Cut small holes in the top to regulate the temp if it gets hotter than 130F.
After a layup, put the part in the 'oven' (the box you made).

[pierre smith]

Then even later, hang strips of thinly sliced meat and dry for jerky.....it works

[RV505]

Originally Posted by Mike S

This is hearsay only--------I am not a chemist, but I have been told that part of the strength of epoxy is that it forms "Long chain" molecules while curing----and that accelerating the cure can interfere with this process.

Any body out there with a chemistry backgorund have input??

Mike

That is what I learned at composite school at the airlines.. Rapid curing makes the part brittle and prone to cracking. a heat lamp ( 18 to 24 inchs away from the part)can be used during the cure... Outside with the sun as a heat source would be acceptable.

[Paul Eastham]

Thanks for the replies. Here are a few warnings in case others want to try this:

1. If the epoxy has not yet started to gel, the heat (even just a little from the sun) will make the epoxy become more fluid. This can cause fillets or even layers of fiberglass to go sliding down and off the work. Wastes the job, and can ruin your table or deck.

2. You can get an uneven cure on thicker buildups, especially if using artificial heat sources. Cured layer with uncured layer underneath. Uncured epoxy in airborne sanding dust = danger. And not so good for sanding.

[Mike S]

Originally Posted by RV505

That is what I learned at composite school at the airlines.. Rapid curing makes the part brittle and prone to cracking. a heat lamp ( 18 to 24 inchs away from the part)can be used during the cure... Outside with the sun as a heat source would be acceptable.

About what I remembered----------warming to lower viscosity---OK, gentle heating to "Post cure"---OK, high heat to "ACCELERATE" CURE-----bad.

Mike